For more or less common knowledge, at least if the majority of the crew has Vehicles(Space) proficiency.

Ships have two speeds: Lets call them Travel Speed and Tactical Speed. (Warp and Impulse for you Trekkies needing a familiar yardstick to compare to.)

In the nature of Phantasy Physics, the approach of a ship under power to another gravity well drops it from Travel speed (100 million miles per day, regardless of ship type) to travel Speed( based on ship type, but generally in the 1MPH to 8 MPH range).

In 3e this was initiated at 25 hexes, but the slowing down period put actual encounter distance at anywhere from 11 to 20 hexes. Keep in mind that, back hen, a hex was 500 tards, or .25 nautical miles. Of course, weapon ranges were much greater back then, at least for Space combat. Gravity is no longer the deciding factor: Time to target is, which makes a certain amount of sense.

Now, 5e leaves it up to the DM with 3 recommended ranges. I split the difference and use Ship's speed. You will drop from Travel to Tactical speed at 1d10+10 rounds of movement. It's 5e, so simple wins out over crunch/logic. Faster ships slow down farther away. Keep in mind that this is based solely on your speed, and you may be much closer (or farther) in time to the other object depending on it's speed, and whether it decides to close, run away, or wait.

Now, the post above covers pretty much everything, but is meant for ship to ship encounters. When traveling through an asteroid field,. it can rather feel like an amusement park ride. and take an unexpected amount of time, depending on density of the field.

As soo as you are about 20 rounds (at full speed for your ship) away from an asteroid you slip into Travel speed...until you suddenly drop out as you come to close to another asteroid. Start and Stop, Speed and Slow, that is travel through an asteroid field, and it's enough to drive a Helmsman to drink, so control on duty access to grog. No drinking and driving. Your best bet is to angle your path up or down from the plane of the ecliptic. A couple million miles either way should miss most of the field. Ten Million is almost certainly safe, and only adds a few hours to a trip that will probably take a couple of days int he first place. The trip directly through the asteroid field will likely take longer, truthfully.

For long distance travel this would be expected as a matter of course. Automatic. However, there are always exceptions. Sometimes you WANT to travel the jerky amusement ride that is asteroid flying. A small planet, such a Ceres may reside in the asteroid field/belt. Bases may, and generally DO. Where else could they even be built, after all? Halflings known as Rock Hoppers have communities in clusters of asteroids in asteroid belts. Dwarves mine out an asteroid and leave a ready made dungeon or wizards/mercenary companies' private base behind. Asteroids can be lucrative areas to fly and work, but they can be hell on Helmsmen.